Oxides of sulfur, such as sulfur dioxide and sulfur trioxide are components of many gaseous effluents such as chemical processes and stack gases from the boilers of coal fired electric power plants. These oxides of sulfur are noxious to human, animal and plant life and are unacceptable for discharge into the atmosphere. Many attempts have been made to successfully remove these gases from stack effluents to protect the atmosphere and to recover the sulfur value as elemental sulfur and recycle the alkali metal carbonate to the gas scrubbing system. The companion necessity to conserve energy has compounded the problem of pollution control, particularly with respect to the recovery of sulfur from stack gases.
Some processes for cleaning these effluent gases and recovering the sulfur values are described in U.S. Pat. Nos. 3,574,530 and 3,883,639, for example. The process described in U.S. Pat. No. 3,574,530 involves the reduction of calcium sulfate sludge with carbon and recovery of sulfur, but fails to provide for the economic utilization of the energy involved and minimization of the cost for such recovery. U.S. Pat. No. 3,883,639 discloses the advantages of using a soluble sulfate, especially magnesium, in the calcium carbonate scrubbing solution, but does not address itself to the recovery of sulfur values.
While these prior art processes are favorable, the economic and ecological advantages of this invention are not described.
Accordingly, a method for removing sulfur dioxide from waste gases and providing for efficient recovery of the sulfur and alkaline earth metal values of the system, while efficiently utilizing the energy necessary for such recovery, would be a significant advance in the art.
Therefore, it is an object of this invention to reduce the sludges containing alkaline earth metal sulfates and/or sulfites produced in wet scrubbing systems to the corresponding sulfide and, at the same time, utilize the heating values of the effluent gases from such reduction reaction to improve the overall economy of the gas cleaning process.
It is an object of this invention to produce a gas in the reduction reaction having sufficient heating value to dry the sulfate/sulfite mixture prior to reduction of same to recover the corresponding alkaline earth metal sulfide.
Other objects and advantages of the described invention will be apparent to those of ordinary skill in the art from the description hereof.